1. Field of the Invention
The present invention relates to a recording element substrate and a recording head including the recording element substrate.
2. Description of the Related Art
FIG. 8 is a diagram illustrating the structure of a recording element substrate discussed in Japanese Patent Application Laid-Open No. 2002-79671. A substrate 300 includes a heater and a drive circuit that are integrally formed by a semiconductor process. A heater array 302A including a plurality of heaters is arranged along an ink supply port 301. A sub-heater 3011 heats the substrate 300 and a temperature detection unit 304 detects the temperature of the substrate 300. Power or signals are input from the outside of the substrate 300 to terminals 305. A drive circuit 303 drives the heaters.
As described above, the drive circuit 303 includes a metal-oxide semiconductor (MOS) transistor whose operation characteristics are changed by heat. Therefore, when the sub-heater 3011 is arranged close to the MOS transistor, the operation of the MOS transistor is likely to be affected by heat generated from the sub-heater 3011. FIG. 12 is a graph illustrating the relationship between a variation in voltage (horizontal axis) between the gate and the source of the MOS transistor and a variation in drain current (vertical axis). When the temperature is changed, voltage-current characteristics are changed.
The operation of a logic circuit is also affected by the temperature. For example, a variation in the speed of a circuit was simulated. As a result of the simulation, one period was about 65 ns (nanosecond) at a temperature of 25° C. and one period was about 90 ns at a temperature of 100° C. The period at a temperature of 100° C. was 1.5 times longer than that at a temperature of 25° C. Thus, when the response speed of a logic circuit is decreased by heat, an error is likely to occur in the operation of the logic circuit.